Breaking out of a foreach loop from within a switch block

Question

How do you break out of a foreach loop while within a switch block?

Normally, you use break but if you use a break within a switch block it will just get you out of a switch block and the foreach loop will continue execution:

foreach (var v in myCollection)
{
    switch (v.id)
    {
        case 1:
            if (true)
            {
                break;
            }
            break;
        case 2;
            break
    }
}

What I'm currently doing when I need to break out of the foreach while within the switch block is setting a bool value placed outside of the loop to true and checking the value of this bool every time the foreach is entered and before entering the switch block. Something like this:

bool exitLoop;
foreach (var v in myCollection)
{
    if (exitLoop) break;
    switch (v.id)
    {
        case 1:
            if (true)
            {
                exitLoop = true;
                break;
            }
            break;
        case 2;
            break
    }
}

This works but I keep thinking there must be a better way of doing this I am unaware of...

EDIT: Wonder why this was not implemented in .NET the really neat way it works in PHP as mentioned by @jon_darkstar?

$i = 0;
while (++$i) {
    switch ($i) {
    case 5:
        echo "At 5<br />\n";
        break 1;  /* Exit only the switch. */
    case 10:
        echo "At 10; quitting<br />\n";
        break 2;  /* Exit the switch and the while. */
    default:
        break;
    }
}

Answer 1

Honestly? This is perhaps the only situation where it is completely valid and proper to use goto:

foreach (var v in myCollection) {
    switch (v.id) {
        case 1:
            if (true)
                // document why we're using goto
                goto finished;
            break;
        case 2;
            break
    }
}
finished: // document why I'm here

Answer 2

You could extract your foreach cycle to the separate method and use return statement. Or you could do like this:

        foreach (object collectionElement in myCollection)
        {
            if (ProcessElementAndDetermineIfStop(collectionElement))
            {
                break;
            }
        }

        private bool ProcessElementAndDetermineIfStop(object collectionElement)
        {
            switch (v.id)
            {
                case 1:
                    return true; // break cycle.
                case 2;
                    return false; // do not break cycle.
            }
        }

Answer 3

Lame, I know, but that's all you can do about it.

You could always transform it into a while loop and add 'exitLoop' as a condition which must be met. Inside the switch, you can call continue to skip the rest of the current pass and since you would have set exitLoop to false, it'd exit much like break would do. Even though it's not exactly what you're asking, perhaps it's more elegant that way?

Answer 4

There's always the option of restructuring your code so that you can return from the switch statement.

Answer 5

Your solution is pretty much the most common option in this case. That being said, I'd put your exit check at the end:

bool exitLoop;
foreach (var v in myCollection)
{
    switch (v.id)
    {
        case 1:
            if (true)
            {
                exitLoop = true;
            }
            break;
        case 2;
            break
    }

    // This saves an iteration of the foreach...
    if (exitLoop) break;
}

The other main option is to refactor your code, and pull the switch statement and foreach loop out into a separate method. You could then just return from inside the switch statement.

Answer 6

Based on MSDN documentation on the break statement, it only allows to stop the top-most scope.

This case is one where you could use a goto statement to leave your foreach loop. If you don't want to use a goto statement, your solution seems to be the best one.

As a side note, you could improve your code by testing the exitLoop flag at the end of the iteration, saving the cost of one enumerator call.

Answer 7

The boolean is one way. Another is using labels and goto. I know folks consider goto to be a cardinal sin, but used judiciously (VERY judiciously), it can be useful. In this case, place a label just past the end of the foreach loop. When you want to exit the loop, simply goto that label. For example:

foreach(var v in myCollection) {
    switch(v.Id) {
        case 1:
            if(true) {
                goto end_foreach;
            }
            break;
        case 2:
            break;
    }
}
end_foreach:
// ... code after the loop

EDIT: some people have mentioned taking the loop out into a separate method so that you can use return. I see the benefit of this as it doesn't require goto and it also simplifies the original function that contained the loop. However, if the loop is simple and is the primary purpose of the function that contains it, or if the loop makes use of out or ref variables, then it's probably best to just leave it in place and use the goto. In fact, because the goto and the label stand out, it probably makes the code clearer rather than clunkier. Putting it in a separate function could make simple code harder to read.

Answer 8

It's not really different from your exitLoop flag, but it might be more readable if you extract a method...

foreach (var v in myCollection)
{
    if(!DoStuffAndContinue(v))
        break;
}


bool DoStuffAndContinue(MyType v)
{
    switch (v.id)
    {
        case 1:
            if (ShouldBreakOutOfLoop(v))
            {
                return false;
            }
            break;
        case 2;
            break;
    }
    return true;
}

Answer 9

If you want to check if any id in myCollection is equal to 1, as per your second example why just don't use myCollection.Any(x => x.id == 1);
Maybe it wasn't what you wanted to do but maybe it gives another angle on the problem...

Answer 10

Some languages (i know PHP is one, not sure about others) allow you to specify how many control structures you'd like to break out of with

break n;
where 1 is implied if you just do break

break 2 would do what you describe, were it available in C#. I don't believe that's the case so your exit flag is probably the best solution.